OSPF Design: Understanding OSPF Areas

OSPF Design - Understanding OSPF Areas

• OSPF areas are crucial to understanding OSPF design, and OSPF areas are divided into two types: Area 0 (backbone) and other areas (1-4.2 billion).
• OSPF areas are introduced to limit LSA (Link State Advertisement) propagation to specific areas, reducing the need for every router to update its network map.

Benefits of OSPF Areas

• OSPF areas allow routers to maintain a separate link state database for each area, reducing unnecessary updates.
• Areas prevent routers from having to recalculate their network maps every time a change occurs in the network.

OSPF Area Hierarchy

• OSPF areas create a two-tier hierarchy, with Area 0 (backbone) at the top and other areas (1-4.2 billion) below.
• Communication between areas must traverse through Area 0, ensuring a loop-free area topology.
• This design creates a hub-and-spoke topology, with Area 0 as the hub and each area as a spoke.

Types of OSPF Routers

• Internal Routers: Routers with all interfaces in a single area.
• Backbone Routers: Routers with at least one interface in Area 0.
• Area Border Routers (ABRs): Routers with one or more interfaces in Area 0 and one or more interfaces in another area.
• Autonomous System Border Routers (ASBRs): Routers that perform redistribution from a foreign routing protocol into OSPF.

OSPF Router Roles

• Internal Routers: Routers 1, 2, 5, 6, and 7 are internal routers in this topology.
• Backbone Routers: Routers 1, 2, 3, and 4 are backbone routers.
• Area Border Routers: Routers 3 and 4 are ABRs, maintaining separate link state databases for each area.
• Autonomous System Border Routers: Router 7 becomes an ASBR when redistributing routes from a foreign routing protocol into OSPF.

OSPF Areas

• OSPF areas are divided into two types: Area 0 (backbone) and other areas (1-4.2 billion).
• OSPF areas limit LSA (Link State Advertisement) propagation to specific areas, reducing the need for every router to update its network map.

Benefits of OSPF Areas

• OSPF areas allow routers to maintain a separate link state database for each area, reducing unnecessary updates.
• Areas prevent routers from having to recalculate their network maps every time a change occurs in the network.

OSPF Area Hierarchy

• OSPF areas create a two-tier hierarchy, with Area 0 (backbone) at the top and other areas below.
• Communication between areas must traverse through Area 0, ensuring a loop-free area topology.
• This design creates a hub-and-spoke topology, with Area 0 as the hub and each area as a spoke.

Types of OSPF Routers

• Internal Routers: have all interfaces in a single area.
• Backbone Routers: have at least one interface in Area 0.
• Area Border Routers (ABRs): have one or more interfaces in Area 0 and one or more interfaces in another area.
• Autonomous System Border Routers (ASBRs): perform redistribution from a foreign routing protocol into OSPF.

OSPF Router Roles

• Internal Routers: have all interfaces in a single area and do not connect to other areas.
• Backbone Routers: connect to Area 0 and enable communication between areas.
• Area Border Routers: maintain separate link state databases for each area and connect multiple areas.
• Autonomous System Border Routers: connect OSPF to other routing protocols and enable route redistribution.